Uhf antenna multicoupler system or the like



July 28, 1959 J. w. MARSHALL ETAL' 7,

UHF ANTENNA MULTICOUPLER SYSTEM OR THE LIKE Filed Feb. 7, 1956 SSheets-Sheet l MIG TRANSMITTER 0R RECEIVER La T0 T0 L TRANSMITTERANTENNA (0R REFOEVER) E 3.6

F l G r3- FREQUENCY AT PARALLEL RESONANCE F IC 4- f HAROLD W. COWAN'ziffi'ig JAMES W. MARSHALL FREQUENCY AT SERIES INVENTORS RESONANCERESONANCE THEIR ATTORNEY July 28, 1959 J. w. MARSHALL ETAL 2,897,499

UHF ANTENNA MULTICOUPLER SYSTEM OR THE LIKE Filed Feb. 7, 1956 L 5 mm. 05 2 t fim M C O F- AE 4 MR 2 T V 2 T m D W H 3 v S M C 0 F. L30. mm M RN H R m Rm 7 E E 0 TV wm N R N MR mw B tflu-% THEIR ATTORNEY July28,1959 J. w. MARSHALL ETAL UHF ANTENNA MULTICOUPLER SYSTEM OR THE LIKE3- Sheets-Sheet 3 Filed Feb. 7, 1956 HAROLD w. COWAN JAMES W. MARSHALLIN V EN TORS fl THEIR ATTORNEY United States Patent UHF ANTENNAMULTICOUPLER SYSTEM OR THE LIKE James W. Marshall, Long Beach, andHarold W. Cowan,

Gardena, Califi, assignors to Hoffman Electronics Corporation, acorporation of California Application February 7, 1956, Serial No.563,920

'12 Claims. (Cl. 343-850) This invention is related to UHF antennamulticoupler systems employable in multiplexing systems which providefor a single antenna a plurality of transmitter or receiver channels orpaths, and more particularly to a new and improved UHF antennamulticoupler system which will insure adequate channel isolation of theorder of 60 db for channel frequency spacings of 3 mc. in the frequencyspectrum of 225-400 me, for example, and yet exhibit a low channelinsertion loss of the order of 1 db or less for each channel when inresonance. The above de-coupling figure (60 db) is deemed to be ample toprevent receiver signal distortion when a high powered transmitter isadjacent a high sensitivity receiver.

In the past, there have been devised many types of UHF antennamulticoupler systems. The most common type is the conventional filtermultiplexing system in which tunable cavity filters are disposed inseries or in parallel with respect to each other. Obviously, for economyof bandwidth the central frequency of the several cavity filters shouldbe as close to one another as possible; yet, for such systems, it hasbeen found that a filter spacing of me. or more may be required toachieve a decoupling figure of the order of 30 db, which of course isnot enough to prevent substantial receiver signal overload wherera highpower transmitter is operating on a channel adjacent to that to which alocal high sensitivity receiver is tuned.

A second and more recent antenna multicoupler system employs the bridgeprinciple with the antenna, a resonant cavity, a balance circuit, and ananti-resonant cavity forming the four legs of the bridge, with thetransmitter or receiver being coupled across first and second oppositejunctions of the bridge and the next coupler coupled across the thirdand fourth opposite junctions of the bridge. The bridge is balanced bythe appropriate adjustment or design of the balanced control circuit forthe resonant and anti-resonant frequencies of each respective bridge.With the bridge in balance, substantially no energy is transmitted tothe succeeding coupler since the third and fourth opposite junctionpoints will be substantially at the same 'instaneous potential, owing tobridge balance.

This second, bridge-type system has .proven .to 'be a considerableimprovement over the first type of multicoupler; however, presentdesigns of the bridge-type multicoupler employ a resonant cavity whichis excited to series resonance, either by end-feeding the stub or byfloating the stub, i.e. by removing the base of the stub from its groundplane. Physical realization of the bridge employing a series-resonantresonant cavity leg has proven exceedingly difficult and involves thedesign of a double coaxial system in which it is impractical to couplemechanically temperature compensation devices to the tuning stubs "ofthe resonant and anti-resonant cav- Also, the necessary capacitivecoupling .of the series-resonant cavity necessarily results in anunsymmetrical cavity response curve generally resembling that of acrystalinasmuch as the series and parallel resonances Patented July 28,1 959 of the cavity occur at closely spaced frequencies. It would ofcourse be highly desirable to improve the response curve of the resonantcavity so that it might be more symmetrical with respect to the Q at thecavity frequency. It would also be desirable to realize a satisfactoryembodiment for the bridge, by which temperature compensating means maybe applied directly to the tuning stubs of both the resonant and theanti-resonant cavities.

Therefore, it is an object of the present inventionto provide a new anduseful UHF antenna multicoupler system.

It is a further object of the present invention to provide a new anduseful UHF antenna multicoupler system which will admit of theincorporation therewith of temperature compensating means or devicesexteriorly' associated therewith and thus not require the employment ofzero-expansion metal combinations.

It is another object of the present invention to provide a new anduseful resonant and anti-resonant cavity combination which will exhibitan optimum response curve for its associated frequency band.

It is a still further object of the present invention to provide a newand useful UHF antenna multicoupler system employing a plurality ofintercoupled bridge networks each of which exhibits a low insertion lossat the coupler frequency of the order of 1 decibel or less and alsowhich exhibits inter-channel isolation of the order of 60 decibels ormore.

According to the present invention, the resonant cavity leg of eachbridge network comprises a stub-tuned cavity operated at parallelresonance. The resonant and antiresonant cavities are inter-associatedin a physical embodiment thereof avoiding concentric, coaxialconfigurations, thus lending the combination to direct, tuning stub,mechanical coupling to temperature compensation devices exterior to thecombination, if desired and as needed. Being excited in parallelresonance, the resonant cavity leg of the bridge exhibits a symmetricalresponse curve and relies upon the high impedance of the circuitincluding the anti-resonant cavity when in parallel resonance forsupplying maximum energy or, in the case of a receiver, receivingmaximum energy from the antenna leg .of the bridge. At the frequency ofthe next channel (which is equal to the series resonant frequency of theanti-resonant cavity leg of the first bridge) a condition exists in thefirst bridge such that 60 decibels or more isolation will exist betweenthe first bridge and the second bridge (which has been excited toresonance). Insertion losses of the several cavity bridges are, at thecavity frequency of parallel resonance, of the order of l decibel orless. Realization of the anti-resonant cavity leg configuration isachieved in a novel manner.

The features of the present invention which are be lieved to be novelare set forth with particularity in the appended claims. The presentinvention, both as to its organization and manner of operation, togetherwith fur-therobjects and advantages thereof, may best be understood byreference to the following description, taken in connection-with .theaccompanying drawings, in which:

Figure 1 is 'a block diagram of the fundamental bridge network employedby the present invention.

Figure .2 is a block diagram of a plurality of intercoupled bridgenetworks, similar in each network to the network of Figure 1.

Figure 3 represents an equivalent circuit of the network of Figure 1.

Figure 4 is a diagrammatic representation of the response curve of the('R') resonant cavity.

Figure 5 is a diagrammatic representation of the response curve of the(AR) anti-resonant cavity.

Figure 6 is a perspective View of the resonant cavity, anti-resonantcavity combination of the present invention.

Figure 7 and Figure 8 are detailed views of certain portions of theapparatus in Figure 6.

In Figure 1 is shown in block diagram the fundamental bridge networkemployed by the present invention. The four arms of the bridge includeantenna 10, resonant cavity (R) 11, balance control circuit 12, andantiresonant cavity (AR) 13. Junction points 14 and 15 are adapted forcoupling to terminals 16 and 17, themselves adapted for coupling to atransmitter or receiver, and junction point 15 is grounded. Junctionpoints 18 and 19 of the bridge are coupled, respectively, to terminals20 and 21, which themselves are adapted for coupling to the next couplerbridge. A more detailed description of resonant cavity (R) 11 andanti-resonant cavity-(AR) 13 shall be given hereinafter.

The operation of the circuit of Figure 1 is as follows. For a givencentral frequency the bridge may be balanced by the appropriateadjustment of balance control circuit 12. When the bridge is in balance,the energy translated to the next or preceding coupler bridge (if atransmitter is coupled to terminals 16 and 17) will be at a minimum, andthere will be a maximum transfer of energy to antenna 10. Suppose nowthat electrical energy is supplied across terminals 20 and 21 at afrequency at which the impedances of resonant cavity 11 and, inparticular, anti-resonant cavity 13, are materially reduced as forexample if anti-resonant cavity 13 is series resonant at this newfrequency. In such a case, substantially all of the electrical energyfrom this source will be coupled directly across antenna 10, owing tothe low resistance of cavity 13 when in a series resonant condition andthe high resistance of the resonant cavity path. By virtue of the uniqueconstruction of the antenna coupler (hereinafter described in detail)the insertion loss of the bridge of Figure l with respect to a signalfrequency 3 megacycles removed from the Figure 1 bridge frequency willbe of the order of l decibel or less.

It is to be noted in Figure 1 that cavity 11 is termed (parallel)resonant cavity 11, or the (R) cavity, and that cavity 13 is termed theanti-resonant (parallel resonant) cavity system 13, or (AR) cavity 13.The (R) and (AR) designation of the resonant cavity and theanti-resonant cavity system are conventional in the art. It should benoted and shall be hereinafter explained that while resonant cavity 11,if in resonance, operates only in parallel resonance, yet theanti-resonant cavity system 13 will operate either in parallel resonanceat the bridge frequency in conjunction with a choke shunting the cavityor will operate in series resonance at that frequency of the adjacentchannel. It shall be demonstrated hereinafter that, by virtue of theabove operation of the antiresonant cavity, the operation of the antennamulticoupler system is made possible.

In Figure 2, several bridge networks are coupled in tandem as shown,i.e. bridge networks 200, 201, and 202. Associated with the severalbridge networks are terminals adapted for coupling to a respectivetransmitter or receiver, terminal 203 and 204, terminals 205 and 206,and terminals 207 and 208. It is to be noted that each of the threebridge networks shown is identical except for the non-inclusion ofantenna 209 in the fourth legs of bridge networks 200 and 201 directly,but in actual fact it is indirectly included therein. By referring tothe discussion relating to Figure 1, the operationof the tandem bridgenetworks of Figure 2 becomes apparent; also the fact that additionalbridge networks may be added, as the, multi-channel system requires.Consider a signal at frequency f being applied across terminals 207 and-208, a signal at frequency f applied across terminals 205 and 206, and asignal at frequency f applied across terminals 203 and 204. Consideralso that the resonant and anti-resonant cavities are both parallelresonant at that signal frequency directly supplied each respectivebridge. Consider also that the anti-resonant cavity is series resonantat the frequency of the adjacent bridge. In such a case, signalfrequency 3; will be translated to antenna 209 with perhaps a halfdecibel loss. Signal frequency f will be translated to antenna 209 withtwo times the half decibel loss or about a loss of 1 decibel, owing tothe fact that two bridge networks will add their insertion losses. Anadditional half decibel loss may be encountered by signal frequency f,owing to an additional bridge network being involved in the translationcircuit to the antenna. It is to be noted, however, that since eachanti-resonant cavity is series resonant for the preceding frequency thatoptimum transfer of energy to the antenna is assured, owing to maximumbridge unbalance for the preceding frequency, and also low insertionloss will be preserved.

In Figure 3 is shown an electrical equivalent circuit of the blockdiagram of Figure 1, excepting however the conjugate matching, balancecontrol circuit 12, which will comprise of course a conventional RLCbalance circuit. The (R) cavity 11 is shown to comprise a 'simple,double inductance, parallel resonant circuit to which are coupled groundadjacent, low impedance ooupling, inductive probe portions 300 and 301of quarter wave length lines 302 and 303, respectively. Quarter wavelength lines 302 and 303 are coupled, respectively, to antenna terminal304 and to transmiter or receiver terminal 305, respectively. Antennaterminal 304 is also coupled to next coupler terminal 306. Transmitteror receiver terminal 305 is in addition coupled, preferably through timedelay line 320, to balance control circuit terminal 307. The inclusionof delay line 320 will compensate for the time delay experienced betweenthe terminals 304 and 305 by virtue of the shift in time across thecenter-grounded combination of quarter wave resonant lines 302 and 303.The remaining next coupler terminal 308 and the remaining balancecontrol circuit terminal 309 are each coupled to terminal 310 ofresonant circuit 311. The remaining terminal 312 of resonant circuit 311is connected to ground. Resonant circuit 311 includes (AR) cavity 313which is or may be excited to series resonance and choke 314, coupledacross (AR) cavity 313.

The operation of the circuit of Figure 3 is best considered after adiscussion of the graphs of Figures 4 and 5. Figure 4 illustrates bycurve 400 the admittance (1/Z)--, frequency response curve of thecombination of circuit 11 and quarter wave lines 302 and 303 in Figure3. Cavity Qs well above 1000 may of course be easily attained. Thus, ator near the frequency of parallel resonance of circuit 11 there will bea maximum translation of energy between antenna terminals 304 and 315and transmitter or receiver terminals 305 and 316. Quarter wave lines302 and 303 are of course designed to be resonated at the parallelresonant frequency of circuit 11. At the parallel resonant frequency ofcircuit 11 it will of course be desirable to have as high an impedanceas possible between terminals 310 and 312 of circuit 311 so as topreclude tendencies of resonant lines 302 and 303 from being loaded downexcessively, which would lower the input impedances to the antennaterminals and to the transmitter or receiver terminals, thus shortingout the signal energy. Hence, circuit 311 will be designed for parallelresonance at that frequency at which circuit 11 is parallel resonant.Hence, at that frequency, the reactance of capacitance 317 must have anabsolute value which exceeds the absolute value of the reactance ofchoke 314 by an amount equal to the absolute value of the reactance ofinductance 318. Hence, inductance 318 will be resonated out of circuit311 at the parallel re O- nant frequency of circuit 11. Now for anincreased value in operating frequency there will be a point at whichthe absolute values of the reactances of capacitance 31] and inductance318 will be e ual; 11 1%, leg 319 of circuit 311 will exhibit seriesresonance and will shunt out choke 314. It of course would be highlydesirable to design leg 319 for series resonance at that frequency atwhich the adjacent channel bridge (see Figure 2 for example) exhibitsparallel resonance. In such a case, for that frequency of the adjacentcavity bridge at which that bridge becomes parallel resonant, not onlymay one rely upon a high Q of cavity circuit 11 in Figure 3 but alsocircuit 311 will be series resonant at that frequency, thus shorting outin efiect any tendencies of circuit 311 to resonate at this newfrequency and also reducing the input impedance to the antenna terminalsand to the transmitter or receiver terminals. These combined ef fectsoperate to give extremely high channel isolation figures, of the orderof 60 decibels, while not appreciably alfecting over-all attenuation ofthe several transmission paths of each frequency source or receiver tothe antenna. A typical response curve for the choke 314, leg 313 circuitis illustrated in Figure 5 by curve 500.

Figure 6, Figure 7, and Figure 8 illustrate the manner in which physicalrealization of the circuit of Figure 3 may be obtained. In Figure 6, (R)cavity 600 in eludes variable tuning stub 601 and tuning knob 602. (AR)cavity 603 includes tuning stub 604 and tuning knob 605. Of course,rather than employing manual tuning knobs, the two cavities might justas easily have had their tuning stubs coupled through temperaturecompensating devices to mechanical tuning apparatus. Resonant lines 606and 607 correspond to resonant lines 302 and 303, respectively, inFigure 3. Inductive probes 6,00: and 609 correspond to inductive probes300 and 301, respectively, in Figure 3. It is to be noted that inductiveprobes 608 and 609 are grounded to the base of cavity 600 at points 610and 611, respectively. The reason that grounding point 611 is locatednear to. tuning stub 601 and yet ground 610 is located relatively faraway from tuning stub, 601 is. (referring again to Figure 3) tocompensate for the 90 phase lag arising from transformer coupling ineach leg in Figure 2. In Figure 6 again, were the inductive probes to bemere opposites with respect to tuning stub. 601, the phase lag producedby the effective transformer coupling would be 180, rather than 0 as iscontemplated by the present configuration. Brief mention is now made ofFigure 7 which shows that resonant lines 60.6. and 607 include lineportion 700, insulating portions 701, shielding portions 702, andinsulating portion 703. While this configuration for the resonant linesis deemed to be desirable, yet the outer insulating portion may bedeleted, if desired. Shielding 702' is of course grounded to cavity 603by means of element 704 having end portion 705. Conductor portion 700may be. provided with pin insert connector 706.

Referring again to Figures 6 and 7, it is shown that several elements704 with adjoining elements 705 are provided to connect electricallycoaxial shield 702 of Figure 7 not only to (R) cavity 600 but also toT-junction member 612, which itself is affixed to cavity 603 by means offlanges 613 and 614 and screw elements 615. Antenna and transmitter (orreceiver) coaxial receptacles 616 and 617, respectively, may be aflixedto T-junction member 612 in a conventional manner. The next coupler andbalance control circuit coaxial receptacles 618 and 619, respectively,may be mounted to bottom portion 620 of cavity 603 through insulatingmember 621 which insulates the receptacles from each other and frombottom portion 620. That such insulation is required is clearly shown inFigure 3 in which, at the parallel resonant frequency of circuit 311,terminal 310- will be isolated from ground by a high impedance.

The intereoupling of the several coaxial receptaclesv with resonantlines 606. and 607 is illustrated in Figure; 8. In Figure 8 is shownagain tuning knob 605 and adjustable or alig-nable tuning stub 604.Affixed to tuning stub 604 is T-junction device 800 having horizontaland vertical portions 801 and 802, respectively. Preferably,

each portion 801 and 802 of T-junction device 800 is coaxial havingconnecting lines 803 and 804 which are adapted for direct connection tocoaxial receptacles 618 and 619 in Figure 6, these coaxial linesbeinghoused within an insulating body portion 805 and an exterior metal shell806. Pin receptacles 807 are each adapted to accommodate the insertionof pins 706 associated with resonant lines 606 and 60.7. Pin receptacles807 are also connected electrically to the center conductors of coaxialreceptacles 616 and 617, by means of leads 809 and 810, respectively.The elements 805' and; 806' of portion 802 are for all intent andpurposes the same as or similar to the corresponding elements of portion801. Of particular importance is the fact that the outer eoaxial shieldsof coaxial lines 803 and 804 may be connected directly to outer shells806 and 806' by means of solder or other metallic means. See for exampleend portions 808 and 808'. The central leads of the coaxial lines are ofcourse insulated from their respective coaxial shields. It should now bepossible to visualize the physical disposition and electricalintereoupling of T-junction device 800 within T-junction member 612 inFigure 6.

The operation of the coupler shown in Figure 6, Figure 7, and Figure 8,is as follows. Refer also to Figure 3. The tuning stubs 601 and 604 maybe adjusted in a conventional manner for cavity resonance at a desiredfrequency, namely, the bridge frequency at which both cavities are to bein effect in parallel resonance. Thus, for an appropriate adjustment of(R) cavity tuning stub 601, a transmitter, for example, coupled throughcoaxial receptacle 616 will excite (R) cavity 600 to resonance, that is,to parallel resonance. from cavity 600 by means of is a portion ofquarter-wave length resonant line 607, which in turn is coupled toantenna coaxial receptacle 616. At this particular frequency, it will ofcourse be desirous to have the (AR) cavity system operate in parallelresonance, although in fact the cavity is excited, or is to be excited,in series resonance. At this point the T-junction device 800 of Figure 8comes into play, for the outer metallic shells 806 and 806' togetherwith end portions 808 and 808 operate as a single, ultra high frequencychoke. That is, by reason of the skin-effect con duction of the outershell surfaces and their leading back to the ground plane of cavity 603,a choke or inductance is inserted in parallel with the series resonantcavity, or otherwise series resonant cavity, as is shown in Figure 3.The inductance of this choke and the design of the (AR) inductive probe609 which cavity itself is such as to operate as the parallel resonantcircuit of Figure 3 (circuit 311) when excited by a signal frequencyassociated with its particular bridge network. However, for a particularhigher frequency, namely the series resonant frequency of cavity 603(which frequency is identical to the natural cavity bridge frequency ofthe next adjacent bridge) the choke inductance exhibited by theT-junction device will in efi'ect be shorted out by the series resonantcavity at this new frequency so that, as has been heretofore explained,the first bridge network will impose only negligible attenuation uponthe signal frequency from the adjacent bridge network whereas bridgenetwork isolation as far as resonant tendencies are concerned will bevery high.

Particularly with reference to Figure 6, it is seen that the physical,embodiment of the circuits of Figure l and Figure 3 is relativelysimple, and adaptable to temperature compensating devices extant, animportant contrast to the prior. art.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects, and, therefore, the aim in theappended claims is:

to cover all such changes and modifications as fall within the ruespirit and. scope of invention.

We claim:

The signal may be coupled 1. In combination, a first cavity having anadjustable tuning stub, a second cavity having an adjustable tuning stuband disposed in proximity with respect to said first cavity, first meansfor coupling energy to said first cavity, second means for couplingenergy from said cavity, first, second, third, and fourth coaxialreceptacles fixedly disposed with respect to said second cavity, saidthird and fourth coaxial receptacles being insulated from said secondcavity, said coaxial receptacles each having a central connector, saidcentral connector of said first coaxial receptacle coupled to said firstmeans, said central connector of said second coaxial receptacle coupledto said second means, and choke means intercoupling said third andfourth coaxial receptacles with said first and second meansrespectively, said choke means being fixedly disposed with respect tosaid tuning stub of said second cavity.

2. Apparatus according to claim 1 in which said first means comprises aquarter wave resonant line having an inductive probe portion inproximity with said tuning stub of said first cavity, and in which saidsecond means comprises a quarter-wave resonant line having an inductiveprobe portion also disposed in proximity with said tuning stub of saidfirst cavity.

3. Apparatus according to claim 1 in which said choke means includes:first and second coaxial coupling lines each having a central leadadapted for respective coupling to said central connectors of said thirdand fourth coaxial receptacles and to said first and second means and acoaxial shield adapted for ground coupling to said second cavity; and anouter shell electrically connected to said coaxial shields of said firstand second coaxial coupling lines and adapted for grounded electricalcontact with said second cavity.

4. Apparatus according to claim 1 in which said first means comprises acoaxial quarter wave resonant line having a central lead provided withan inductive probe portion and a coaxial shield, said coaxial shieldbeing grounded to said first cavity, said first cavity having a firstaperture adapted to admit said inductive probe portion for dispositionwithin said cavity in proximity to said tuning stub, said inductiveprobe being grounded to said first cavity at a remote point with respectto said tuning stub; and in which said second means comprises anadditional coaxial quarter wave length resonant line provided with aninductive probe portion and a coaxial shield, said coaxial shield beinggrounded to said first cavity, said first cavity having a secondaperture adapted to admit said inductive probe portion of saidadditional resonant line for disposition within said cavity in proximitywith said tuning stub, said inductive probe portion of said additionalresonant line being grounded to said first cavity at a point near saidtuning stub.

5. Apparatus according to claim 4 in which said choke means includes:first and second coaxial coupling lines each having a central leadadapted for respective coupling to said central connectors of said thirdand fourth coaxial receptacles and to said central leads of said coaxialquarter wave resonant lines and a coaxial shield adapted for groundcoupling to said second cavity; and an outer shell electricallyconnected to said coaxial shields of said first and second coaxialcoupling lines and adapted for grounded electrical contact with saidsecond cavity.

6. A UHF antenna multicoupler bridge network including, in combination:a balance control circuit, a resonant cavity excitable in parallelresonance and having first and second coupling terminals; said balancecontrol circuit being coupled to said first coupling teminal; an antennacoupled to said second coupling terminal; first and second exciter linescoupled between said first and second coupling terminals, respectively,and the internal wall of said resonant cavity, each of said exciterlines having a probe portion supported internally of said cavity, andeach of said lines having an electrical length of substantiallyone-quarter of the resonant wavelength of said resonant cavity; anantiresonant cavity system coupled to said antenna and forming a firstjunction therewith; said balance control circuit being coupled to saidanti-resonant cavity to form a second junction therewith, saidanti-resonant cavity system also being excitable in parallel resonance;third and fourth terminals coupled to said first coupling terminal andsaid first junction, respectively, and adapted for coupling to anelectronic component; and fifth and sixth terminals coupled to saidsecond coupling terminal and said second junction, respectively, andadapted for coupling to associated multicoupler apparatus.

7. Apparatus according to claim 6 in which a delay line is interposedbetween said balance control circuit and said first junction.

8. A UHF antenna multicoupler bridge network including, in combination:a balance control circuit; a resonant cavity excitable in parallelresonance at a first frequency and having first and second couplingterminals; said balance control circuit being coupled to said firstcoupling terminal; an antenna coupled to said second coupling terminal;first and second exciter lines coupled between said first and secondcoupling terminals, respectively, and the internal wall of said resonantcavity, each of said exciter lines having a probe portion supportedinternally of said cavity, and each of said lines having an electricallength of substantially one-quarter of the wavelength corresponding tosaid first frequency; an antiresonant cavity system coupled to saidantenna and forming a first junction therewith; said balance controlcircuit being coupled to said anti-resonant cavity system to form asecond junction therewith, said anti-resonant cavity system beingexcitable in parallel resonance at said first frequency and in seriesresonance at a second frequency; third and fourth terminals coupled tosaid first coupling terminal and said first junction, respectively, andadapted for coupling to an electronic device; and fifth and sixthterminals coupled to said second coupling terminal and said secondjunction, respectively, for coupling to associated multicouplerapparatus.

9. Apparatus according to claim 8 in which a delay line is interposedbetween said balance control circuit and said first junction.

10. A plurality of intercoupled bridge networks including, incombination: a first balance control circuit; a first resonant cavityexcitable in parallel resonance and coupled to said balance controlcircuit to form a first junction therewith; an antenna coupled to saidfirst resonant cavity and forming a second junction therewith; a firstanti-resonant cavity system coupled to said antenna and forming a thirdjunction therewith; said first balance control circuit being coupled tosaid first anti-resonant cavity to form a fourth junction therewith,said first antiresonant cavity system being excitable :in parallelresonance; first and second terminals coupled to said first and thirdjunctions and adapted for coupling to an electronic component; third andfourth terminals coupled to said second and fourth junctions; at leastone additional bridge network, including: at least one additionalantiresonant cavity; at least one additional balance control circuitcoupled to its associated additional anti-resonant cavity system to forma fifth junction therewith; at least one additional resonant cavitycoupled to its associated additional balance control circuit to form asixth junction therewith and adapted for excitation in parallelresonance; each such additional resonant cavity and said first resonantcavity being coupled to each other and to said second junction; saidfourth terminal being coupled to said additional anti-resonant caivtysystem of the next preceding bridge network in said plurality; and saidfifth junction and corresponding junctions of any other of saidadditional bridge networks being coupled to the antiresonant cavitysystem of its next preceding bridge network, if any.

11. Apparatus according to claim 10 in which said resonant cavities areprovided with input and output quarter-wavelength resonant exciter lineshaving probe portions.

12. Apparatus according to claim 10 in which each of said resonantcavities and each of said anti-resonant cavities exhibits parallelresonance at a predetermined common frequency.

References Cited in the file of this patent UNITED STATES PATENTS

